This application claims the Paris convention priority of Japanese patent application 2000 277260 filed on Sep. 12, 2000, the entire disclosure of which is incorporated herein by reference.
i) Field of the Invention
The present invention relates to a phase shift mask blank which is suitable particularly for ArF or F2 excimer laser, and a manufacturing apparatus and method of the phase shift mask blank.
ii) Description of the Related Art
In recent years, it has been clarified that high resolution and focus depth are two important properties required for photolithography but are in a contradictory relation with each other, and that a practical resolution cannot be enhanced only by high NA and short wavelength of a lens of an exposure apparatus (Monthly Semiconductor World 1990.12, Applied Physics Vol. 60, Nov. 1991, and the like).
Under such situation, phase shift lithography has been noted as the next-generation photolithography technique, and partially brought to practical use. The phase shift lithography is a method for enhancing the resolution of photolithography by change only of a mask without changing an optical system. When a phase difference is applied between exposure lights transmitted through the photo mask, mutual interference of the transmitted lights can be utilized to rapidly enhance the resolution.
The phase shift mask is a mask for using light strength information together with phase information. Various types of the masks are known such as Levenson type, auxiliary pattern type, and self-matching type (edge emphasizing type). These phase shift masks have a complicated constitution and require a high degree of manufacturing technique as compared with the conventional photo mask which has only the light strength information.
In recent years, a so-called halftone type phase shift mask has been developed as one of the phase shift masks.
In the halftone phase shift mask, a light semi-transmission portion has two functions: a shield function of substantially shielding the exposure light; and a phase shift function of shifting (usually reversing) a light phase. Therefore, it is unnecessary to separately form a shield film pattern and phase shift film pattern. This type of phase shift mask is simple in constitution and easy in manufacturing.
For the halftone phase shift mask, as shown in FIG. 4, a mask pattern formed on a transparent substrate 100 is constituted of a light transmission portion (transparent substrate exposed portion) 200 for transmitting a light which is strong enough to substantially contribute to exposure, and a light semi-transmission portion (shield and phase shifter portion) 300 for transmitting a light which is not strong enough to substantially contribute to the exposure (FIG. 4A). Additionally, the phase of the light transmitted to the light semi-transmission portion is shifted, and the light semi-transmission portion is brought to a substantially reversed relation with respect to the phase of the light transmitted through the light transmission portion (FIG. 4B). The lights transmitted in the vicinity of a boundary between the light semi-transmission portion and the light transmission portion and turned to the opposite portions by diffraction phenomenon cancel each other. Thereby, light strength in the boundary is substantially set to zero, and contrast, that is, resolution of the boundary is enhanced (FIG. 4C).
The light semi-transmission portion (phase shift layer) in the halftone phase shift mask or blank needs to have a required optimum value with respect to both transmittance and phase shift amount. Concretely, (1) the transmittance in an exposure wavelength of KrF, ArF, or F2 excimer laser, or the like can be adjusted in a range of 3 to 20%, (2) a phase angle can be adjusted usually to a value in the vicinity of 180xc2x0 in the exposure wavelength, and (3) the transmittance needs to be usually testable in a range of 65% or less in test wavelengths such as 257 nm, 266 nm, 364 nm, and 488 nm.
In recent years, there has been a demand for a finer processing of a device, or the like, and shortening of an exposure wavelength for use in the device has been advanced. On the other hand, influences of a particle adhering to the mask blank and a pinhole formed in the mask have been increasingly regarded as problems. That is, for example, by generation of arc in a film formation apparatus during film formation, or other causes, a particle with a particle diameter of about one micron or less is sometimes mixed in the light semi-transmission film at a ratio of about 0.05 to 0.5 particle per one square centimeter. Moreover, when there is a fine groove or hole in the surface of a target, the particle with a particle diameter of about several microns or less is sometimes mixed in the light semi-transmission film. When the particle mixed in the light semi-transmission film falls out in a cleaning process, the pinhole is generated. Therefore, in order to prepare the mask blanks having less pinholes, it is necessary to reduce the number of particles during formation of the light semi-transmission film.
Additionally, in conventional mask blanks for i-ray, or KrF excimer laser, in which a relatively long wavelength is used as the exposure wavelength, there are many particles or pinholes. Therefore, the blanks cannot be applied to some of photo mask blanks for KrF, in which a pattern finer than a conventional pattern is formed, or mask blanks for a short wavelength of ArF or F2 excimer laser.
With the shortening of the exposure wavelength, a property of the particle or the pinhole, required for the mask blanks, becomes stricter. It is necessary for practical use of the mask blanks for the short wavelength of the ArF or F2 excimer laser to reduce the number of particles or pinholes having a diameter larger in size than about a half of the exposure wavelength as much as possible.
The present invention has been developed under the aforementioned background, and a first object thereof is to provide a phase shift mask blank in which the number of particles or pinholes each having a diameter larger than a diameter substantially equivalent in size to an exposure wavelength is reduced as much as possible.
Moreover, a second object of the present invention is to provide a manufacturing apparatus and method able to manufacture the phase shift mask blank in which the number of particles or pinholes each having the diameter larger than the diameter equivalent in size to the exposure wavelength is reduced as much as possible.
Furthermore, a third object of the present invention is to provide a photo mask blank in which the number of particles or pinholes is reduced as much as possible.
Additionally, a fourth object of the present invention is to provide a manufacturing apparatus and method which can manufacture the photo mask blank having the number of particles or pinholes reduced as much as possible.
To achieve the aforementioned objects, the present invention has the following constitutions.
(Constitution 1) A manufacturing method of a photo mask blank having a thin film for forming a pattern on a transparent substrate,
wherein during sputtering formation of the thin film, the surface of a target is directed downwards and the surface of a substrate is directed upwards with respect to a gravity direction, and a peripheral edge of the substrate is shielded in order to prevent film formation.
Particularly, a manufacturing method of a halftone phase shift mask blank having a light semi-transmission film on a transparent substrate,
wherein during sputtering formation of the light semi-transmission film, the surface of a target is directed downwards and the surface of a substrate is directed upwards with respect to a gravity direction, and a peripheral edge of the substrate is shielded in order to prevent film formation.
(Constitution 2) A manufacturing method of a photo mask blank having a thin film for forming a pattern on a transparent substrate, comprising a step of:
manufacturing the thin film using a DC magnetron sputtering apparatus comprising at least a sputtering target, a magnetron cathode with the target attached thereto, a substrate holder disposed opposite to the target, and a shield disposed on an inner wall of a vacuum tank inside the vacuum tank,
wherein the surface of a target is directed downwards with respect to a gravity direction, and
the apparatus has a mechanism for reducing film formation on a non-sputtered area on the target and the surface of the shield.
(Constitution 3) The manufacturing method according to constitution 2 wherein the mechanism for reducing the film formation onto the non-sputtered area on the target comprises a mechanism in which a whole-surface erosion cathode is used as the magnetron cathode, a mechanism for shielding the non-sputtered area on the target, or a mechanism for roughening the surface of a non-sputtered portion on the target.
(Constitution 4) The manufacturing method according to constitution 3 wherein the mechanism for reducing the film formation onto the non-sputtered area on the target further comprises a mechanism for forming a corner in the target into a curved surface, and roughening an end surface of the target.
(Constitution 5) The manufacturing method according to constitution 2 wherein in the mechanism for reducing the film formation on the shield surface, the shield is kept at a constant temperature, and a shape of the shield is designed so that a relative film formation speed t in the following equation (i) in at least a shield position in the vicinity of the target is prevented from being larger than a value in a position on the substrate:
t=cos xcex81xc3x97Sin (xcex81xe2x88x92xcex82)/r2 xe2x80x83xe2x80x83(i) 
(in the equation (i), r denotes a distance between a target center and a shield position, xcex81 denotes an angle of a line connecting the target center to the shield position with respect to a normal of a target plane, xcex82 denotes an angle of a shield plane with respect to the normal of the target plane, and t denotes the relative film formation speed in the shield position defined by r and xcex81).
(Constitution 6) The manufacturing method according to constitution 5 wherein in the mechanism for reducing the film formation onto the shield surface comprises a mechanism for forming a corner in the shield into a curved surface, roughening the surface of the shield, and disposing an earth shield above the target plane.
(Constitution 7) The manufacturing method according to any one of constitutions 2 to 6 wherein the apparatus further comprises a backing plate to which the target is to be attached, and the surface of the backing plate is roughened.
(Constitution 8) The manufacturing method according to any one of constitutions 2 to 7 wherein the apparatus further comprises a shield plate for preventing the film from being formed on a peripheral portion of the substrate.
(Constitution 9) A photo mask blank manufactured using the manufacturing method according to any one of constitutions 1 to 8.
(Constitution 10) A photo mask blank having a thin film for forming a pattern on a transparent substrate,
wherein a total number of particles and pinholes having a diameter larger than a diameter substantially equivalent in size to an exposure wavelength for use in the blank as a mask is 0.1 or less per square centimeter.
(Constitution 11) A photo mask blank having a thin film for forming a pattern on a transparent substrate,
wherein an exposure wavelength for use in the blank as a mask has a center wavelength of 193 nm or less, and a total number of particles and pinholes having a diameter larger than 0.2 xcexcm is 0.1 or less per square centimeter.
(Constitution 12) The photo mask blank according to constitution 10 or 11 wherein the thin film for forming the pattern is a light semi-transmission film, and the photo mask blank is a halftone phase shift mask blank.
(Constitution 13) A manufacturing apparatus of a photo mask blank for carrying out the manufacturing method according to any one of constitutions 1 to 8.
(Constitution 14) A photo mask manufactured by patterning a thin film in the photo mask blank according to any one of constitutions 9 to 12.
(Constitution 15) A pattern transfer method using the photo mask according to constitution 14 to transfer a pattern.
In the constitution 1, when the target plane is directed downwards with respect to the gravity direction, the substrate surface necessarily turns upwards, and the film is formed on the whole surface and side surface of the substrate, but the peripheral edge of the substrate is shielded to prevent the film formation as in the constitution 1. Thereby, particles generated when the film is stripped by handling or cleaning after forming the light semi-transmission film can remarkably be reduced, and yield of the mask is remarkably enhanced. This is necessary particularly for the phase shift mask for the short wavelength of ArF or F2 excimer laser.
According to the constitutions 2 to 6, the generation of the particles from the target plane, shield plane (including the earth shield), or a gap between the target and the earth shield can securely be prevented. Additionally, respective countermeasures according to the constitutions 2 to 6 are effective alone. However, a combination of all the countermeasures can securely prevent the generation of the particles from the target plane, the shield plane (including the earth shield) or the gap between the target and the earth shield.
According to the constitution 7, the generation of the particles from a backing plate portion can securely be prevented.
According to the constitution 8, when the peripheral edge of the substrate is shielded by the shield plate in order to prevent the film from being formed on the peripheral edge of the substrate, the particles generated by the film stripped by handling or cleaning after forming the light semi-transmission film can remarkably be reduced, and the yield of the mask is remarkably enhanced. This is necessary particularly for the phase shift mask for the short wavelength of ArF or F2 excimer laser.
According to the constitution 9, the photo mask blank having few defects can be obtained.
According to the constitution 10, the total number of particles and pinholes having the diameter larger than the diameter substantially equivalent in size to the exposure wavelength for use in the blank as the mask is 0.1 or less per square centimeter. Therefore, practical use of the photo mask for the short wavelength of ArF or F2 excimer laser can be realized. When the number exceeds 0.1, it is difficult to realize the practical use of the photo mask for the short wavelength of the ArF or F2 excimer laser.
Additionally, even in the present situation, the mask can practically be used for KrF excimer laser, but the number of particles and pinholes is further preferably reduced. Therefore, the invention of the constitution 10 can be applied to the photo mask blank for KrF excimer laser, or particularly to some of the photo mask blanks for KrF in which a pattern finer than the conventional pattern is formed. Moreover, the invention can also be applied to a general photo mask blank, because it is preferable to further reduce the number of particles or pinholes.
Here, the substantially equivalent wavelength includes wavelength xc2x120%.
Additionally, the total number of particles and pinholes having a diameter larger in size than about a half of the exposure wavelength is preferably 0.1 or less per square centimeter. This range includes xc2xd wavelength xc2x120%.
According to the constitution 11, the exposure wavelength for use in the blank as the mask has a center wavelength of 193 nm or less, and the total number of particles and pinholes having a diameter larger than 0.2 xcexcm is 0.1 or less per square centimeter. Therefore, the practical use of the photo mask for the short wavelength of the ArF or F2 excimer laser can be realized. Additionally, the total number of particles and pinholes having a diameter larger than 0.15 xcexcm, preferably larger than 0.1 xcexcm is preferably 0.1 or less per square centimeter. This is realized depending upon a limitation of sensitivity of a defect test apparatus. In order to detect the particles and pinholes having smaller diameters, the defect test apparatus with a higher sensitivity is necessary.
According to the constitution 12, the practical use of the halftone phase shift mask for some of KrF excimer lasers in which the pattern finer than the conventional pattern is formed and for the short wavelength of the ArF or F2 excimer laser can be realized.
According to the constitution 13, it is possible to manufacture the photo mask blank having few defects.
According to the constitution 14, the photo mask having few defects can be obtained, and the practical use of the photo mask for some of KrF excimer lasers in which the pattern finer than the conventional pattern is formed and for the short wavelength of the ArF or F2 excimer laser can be realized.
According to the constitution 15, the photo mask having few defects, and the short exposure wavelength of the KrF excimer laser or ArF or F2 excimer laser can be used to realize a fine pattern processing.
The present invention will be described hereinafter in detail.
In order to achieve the aforementioned objects, as a result of pursuing of researches, the following has been found.
Mixture of the particles into the light semi-transmission film during sputtering causes stripping of the film attached in a vacuum tank. The particles caused by the stripped film are generated from a non-sputtered portion of the target surface, a gap between the target and an electrically grounded vacuum tank inner wall (earth shield), a film attachment preventing component (shield) detachably attached to the inner wall of the vacuum tank, and the like.
In order to prevent the particles from being generated from the non-sputtered portion of the target surface, the following countermeasures are effective: (countermeasure 1) a whole-surface erosion cathode or the like is used to reduce an area of the non-sputtered portion on the target; (countermeasure 2) the non-sputtered portion (non-erosion portion) of the target surface is shielded by a shield member; and (countermeasure 3) the non-sputtered portion (non-erosion portion) of the target surface is roughened by blast treatment (treatment for mechanically/physically roughening the surface).
The present invention will be described hereinafter with reference to FIGS. 1 and 2, but these are drawings for simple description of positions to be subjected to the countermeasures, and the apparatus of the present invention is not limited to forms (e.g., shapes and positional relation (distance) of the respective portions) of these drawings.
The generation of the particle from a gap 13 between a target 5 and an earth shield 12 raises a problem, when the whole-surface erosion cathode is used and the end of the target is not shielded with a shield member or the like. In order to prevent the particle from being generated from this gap, the following countermeasures are effective: (countermeasure 4) a portion of a corner 5a in the end of the target is formed into a curved surface (R processed); (countermeasure 5) the blast treatment or another method is used to roughen a target end 5b; (countermeasure 6) the blast treatment or another method is used to roughen exposed backing plate surfaces 4a, 4b; (countermeasure 7) a corner 12a of the earth shield is R-processed; (countermeasure 8) the surface of the earth shield 12 is roughened by the blast treatment or another method; and (countermeasure 9) the earth shield 12 is disposed above a target plane d (on a side of the backing plate 4).
In order to prevent the particle from being generated from the shield portion, (countermeasure 10) improvement of a shield shape is effective as described later.
A formation speed t of the film attached to the shield disposed in the vacuum tank can qualitatively be represented by the equation (i) developed by the present inventor.
t=cos xcex81xc3x97sin (xcex81xe2x88x92xcex82)/r2xe2x80x83xe2x80x83(i) 
Here, respective variables in the equation (i) will be described with reference to FIG. 1. Variable r denotes a distance between a target center a and a shield position c, xcex81 denotes an angle of a line connecting the target center a to the shield position c with respect to a normal e of the target plane, xcex82 denotes an angle of a shield plane 11 with respect to the normal e of the target plane, and t denotes the relative film formation speed in the shield position c defined by r and xcex81. Additionally, the shield 11 has a leaf shape in FIG. 1, but the shield 11 may have the leaf shape or a block shape. Moreover, the shield 11 is electrically insulated from the earth shield 12, the earth shield 12 may be earthed, and a voltage may be applied to the shield 11.
In the shield position c in the vicinity of the target 5 (area in which a value of r is smaller than a distance to the transparent substrate with the light semi-transmission film to be formed thereon), it is effective for prevention of the particle generation to design the shape of the shield 11 so that the relative film formation speed t in the equation (i) is prevented from being larger than the value in the position on the substrate. In order to satisfy the aforementioned conditions, it is necessary to set a sufficient distance (set r to be large) between the shield position c to which many films are attached (xcex81 is small) and the target 5 (i.e., the shield 11 in the vicinity of the target is disposed apart from the target). It is also necessary to reduce an angle xcex83 of the shield plane in the shield position in the vicinity of the target 5 (with small r) with respect to the target plane d (set xcex82 to be large and close to xcex81) (i.e., set the shield plane in the vicinity of the target to be horizontal with the target plane d).
In order to prevent the particle from being generated from the shield portion, (countermeasure 11) to remove (R process) a sharp corner or a sharp screw from a portion to which the film is attached on the shield, and (countermeasure 12) to roughen the surface of the shield by the blast treatment or the like are effective.
Additionally, (countermeasure 13) to hold the shield to which the film is attached by heating at a constant temperature is also effective as means for reducing the particle generated from the shield.
Here, the shield (including the earth shield) in the vicinity of the target is heated by a plasma generated on the target or a sputtered particle from the target. When film formation start and end are repeated, temperature on the shield changes, and stress of the film attached to the shield changes with a temperature change. When the film stress on the shield changes, the film is cracked or stripped, and therefore the particle is mixed into the light semi-transmission film. When the shield is held at constant temperature, the stress of the film is also kept to be constant, and the particles generated from the shield decrease. Optimum temperature of the shield changes with the material of the shield or the type of the film. However, in the present invention, when temperature of the shield is controlled to 160xc2x0 C. from 100xc2x0 C., the number of particles mixed in the light semi-transmission film can be reduced.
When the target surface is directed upwards, the particle adheres to the target surface, this causes abnormal electric discharge, a micro groove and hole are formed in the target surface by the abnormal electric discharge and the abnormal electric discharge is repeated. The film attached to the particle adhering to target surface or the fine groove or hole is heated by the plasma in the vicinity of the target, evaporation and burst are caused, and the particle or impurity is mixed in the light semi-transmission film. On the other hand, when the target surface is directed downwards, the particle does not easily adhere to the target surface, and therefore the abnormal electric discharge does not easily occur. Therefore, in order to form the light semi-transmission film having few particles, a sputter down system in which the target surface is directed downwards is preferable.
Additionally, the particle is sometimes generated by film stripping caused by handling or cleaning after formation of the light semi-transmission film. To prevent this, as shown in FIG. 2, there is (countermeasure 15) a method of disposing the shield plate for shielding a portion 6a for holding a transparent substrate 6 before and after the film formation, and forming no light semi-transmission film on this portion.
Additionally, during attaching of the substrate to the substrate holder, the shield plate can preferably be retreated to a position in which the attaching of the substrate is not inhibited. Moreover, the shield plate is preferably movable so that a clearance between the surface of the substrate with the film formed thereon and the shield plate can be adjusted with high precision (e.g., precision of about 0.1 mm) after attaching the substrate to the substrate holder.
The countermeasures for preventing the particle from being generated in the sputtering apparatus for forming the light semi-transmission film have mainly been described above. However, (countermeasure 16) to automate handling until introducing of the transparent substrate into the sputtering apparatus with a mechanism having little particle generation, or to set an atmosphere of a substrate introduction portion to be in a dust-free state is essential for preventing the particle generation.